1. Field of the Invention
The present invention relates to a communication LSI and, more particularly, a communication LSI for executing processes of a transmission frame with a physical layer capable of responding flexibly to supplements and/or modifications of standard carried out in future.
2. Description of the Prior Art
A concept for providing services for home such as video on demand, TV shopping, remote medical service, ticket reservation etc. and services for enterprise such as high speed data communication, TV conference etc. by connecting homes, enterprises, public facilities, business facilities, public agencies and the like to each other via high speed communication lines using mainly optical fibers is being advanced. In general, this concept is called as B-ISDN (Broadband Integrated Services Digital Network). Projects for constructing nationwide networks in major countries until early 21st century are also being advanced.
Generally, communication protocols are constituted hierarchically. In B-ISDN, a layered structure is formed by physical layer, ATM layer, ATM adaptation layer, and upper layer in order from the bottom.
The physical layer executes processes of photoelectric conversion, bit synchronization, and transmission frame. The ATM layer executes process regarding ATM cell header. The ATM adaptation layer executes conversion between user data and ATM cell. The upper layer executes protocol processes such as connection establishment and connection release.
Now, SDH (Synchronous Digital Hierarchy) is stipulated as the physical layer of B-ISDN by ITU (International Telecommunication Union). Two types of transmission frames are stipulated in SDH, i.e., STM-1 having a transmission rate of 155.52 Mbps and STM-4 having a transmission rate 622.08 Mbps. An explanation will be given hereinafter using STM-1 having a transmission rate of 155.52 Mbps.
The transmission frame of STM-1 has a structure shown in FIG. 1A. The transmission frame is shown to have 270 bytes in the lateral direction and 9 rows in the vertical direction for easy understanding. Actually, the transmission frame is converted into bit stream sequentially from the first byte located on the left end of the first row to the last bye located on the right end of the last row. SOH and AU-4 pointer are arranged as an overhead in leading 9 columns of the transmission frame. Virtual containers called as VC-4 are arranged in remaining portions. In addition, as shown in FIG. 1B, VC-4 has a structure formed of 261 bytes in the lateral direction and 9 rows in the vertical direction. In VC-4, an overhead called as POH is arranged in a leading first column. In VC-4, portions except for POH are called as "payload" wherein ATM cells of 53 bits are mapped.
Next, FIG. 2A shows an arrangement of parameters stored in SOH and AU-4 shown in FIG. 1A. Functions of these parameters are shown in a table of FIG. 3A. Similarly, FIG. 2B shows an arrangement of parameters stored in POH shown in FIG. 1B. Functions of these parameters are shown in a table of FIG. 3B.
In a user network interface which is supposed as an application field of the communication LSI of the present invention, part of the overheads are used as shown in the table of FIG. 3A. In these tables, "NNI" is an abbreviation for Network Node Interface while User Network Interface is abbreviated to "UNI".
Information handled in the physical layer will be shown hereinbelow for convenience sake of following explanations. These are stipulated in TA-NWT-000253, TR-NWT-001112 both issued by Bellcore, and Recommendation I.432 issued ITU-T.